Numerical aperture , definition

One of the methods under development at AT T Bell Laboratories for submicron lithography is deep ultraviolet projection photolithography. (O Fine line definition is obtained by use of 248 nm light and a lens of large numerical aperture. Because of the large chromatic aberration of the quartz lens a spectrally line-narrowed krypton fluoride excimer laser is used as a light source. 

By definition, the numerical aperture of a lens is the sine of one-half its acceptance angle (0), so it follows that the minimum resolvable line width (/ipmin = p/2) should be... 

In microoptics, several types of microlenses have been developed. A spherical microlens is used mostly to gather light from a laser diode by taking advantage of the high numerical aperture and the small Fresnel reflection of light from its spherical surface. Moreover, the precise construction of the sphere is very easy but its mount to a definite position must be considered specially. Spherical aberration is of course large. 

Figure 11.3 Definition of numerical aperture (NA) of objective lens.

Fig. 8j4 Definition of the angle ec, which is important for the numerical aperture NA, and two examples for the variation of the Airy diffraction image as a function of NA. The effective angle, under which the object is seen, amounts to 37° (left-hand side) and 58° (right-hand side).

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